An aortic blood pump, an example of an aortic counter pulsation cardiac assist device, can be permanently surgically implanted in the wall of the aorta to augment the pumping action of the heart. The aortic blood pump is sometimes referred to as a mechanical auxiliary ventricle assist device, dynamic aortic patch, or permanent balloon pump. Alternatively, the aortic blood pump can be inserted using minimally invasive technique, and is sometimes referred to as a temporary balloon pump, or simply as a balloon pump, since extended periods of use are possible depending on the method and location of surgical insertion.
Typically, the aortic blood pump includes a flexible bladder to be inflated and deflated in a predetermined synchronous pattern with respect to the diastole and systole of the patient to elevate aortic blood pressure immediately after aortic valve closure. Inflation and deflation of the bladder can be accomplished by means of a supply tube connected to the bladder and can be connected to a percutaneous access device (PAD). The PAD can be permanently surgically implanted in a patient's body to provide a through-the-skin coupling for connecting the supply tube to an extra-corporeal energizing source. Electrical signal leads from electrodes implanted in the myocardium are likewise brought out through the skin by means of the PAD. The “R” wave of the electrocardiograph and/or feature related to the aortic pressure wave form can be employed to control the fluid pressure source to inflate and deflate the inflatable chamber in a predetermined synchronous relationship with the heart action.
The aortic blood pump acts to assist or augment the function of the left ventricle and is typically restricted to use in patients who have some functioning myocardium. The aortic blood pump does not need to be operated full-time, and in fact, can be operated periodically on a scheduled on-time, off-time regimen. Typically, the patient can be at least temporarily independent of the device for periods of one to four hours or more, since the aortic blood pump does not require continuous operation.
Temporary intra-aortic balloon pumps are generally known for insertion through the femoral artery of the leg for emergency patient treatment. Temporary use of the pump was originally intended to last for only a few hours up to a few days for non-ambulatory patients in emergency situations. The temporary intra-aortic balloon pump is limited in size to prevent fully occluding the lumen of the aorta and/or any branch arteries, so that pressures within each location are free to equalize at all times during the pump inflation cycle, and in order to pass percutaneously via an introduction sheath through the smaller diameter of the femoral artery during insertion. Non-ambulatory patients restricted to bed can subsist with the level of cardiac assistance available from the relatively small (e.g. typically 30 to 40 cubic centimeters (cc)) volume of the temporary intra-aortic balloon pump. However, this relatively limited level of cardiac assistance is insufficient, and the typical location of insertion is undesirable, for ambulatory patients. In addition, the temporary intra-aortic balloon pump is typically tightly furled and wrapped in order to allow for insertion through a narrow introduction sheath. The furling and wrapping of the material raises the concern of damage to the material of the balloon pump, which might lead to premature failure when subjected to numerous pumping cycles, if prolonged use over a period greater than a few days is mandated for a particular patient. Further, the power supply conduit to the pump is of limited cross sectional area because of the use of a helium pumping medium in order to provide the desired level of responsiveness to correctly time the inflation and deflation of the temporary intra-aortic balloon pump with respect to the heart beat of the patient. The use of a helium pumping medium may not be as practical as the use of an air pumping medium in order to provide a simple cardiac assistance device for long term ambulatory patients.
In the original description of clinical use of the temporary IABP, the procedure described the open exposure of the femoral artery with end-to-side anastomosis of a short vascular graft. The graft was used as the vascular entry point. As the use of the temporary IABP grew internationally, many variants of this original concept were introduced to solve specific clinical dilemmas. These variants were introduced to permit use of the temporary IABP in patients with unusually small or stenotic femoral vessels, or in patients whose aorta was easily available during thoracotomy or in patients needing the temporary IABP as a bridge-to-transplant. Distal ischemic complications are a concern in many of these methods. Techniques that use an end-to-side vascular graft may be less prone to this complication. Variant vascular entry points that have been described for the temporary IABP have included: (1) open approach to the femoral artery with cannulation via an end-to-side vascular grafts; (2) percutaneous approach to the femoral artery; (3) open approach to the iliac artery; (4) retro peritoneal approach; (5) during open thoracotomy for a standard open-heart procedures, the open trans thoracic approach with direct cannulation with the aorta; (6) during open thoracotomy for standard open-heart procedures, the open trans thoracic approach with cannulation via end-to-side vascular graft; (7) large aortic caliber side graft for cul-de-sac placement; and (8) axillary artery approach with cannulation either directly or via an end-to-side vascular graft.
To alleviate some of the limitations and difficulties associated with the catheter-based temporary intra-aortic balloon pump, a permanent balloon pump in the form of an elliptical patch supporting the pumping chamber was disclosed in U.S. Pat. No. 4,630,597 for incorporation into the wall of the aorta by a surgeon. Permanent use of the pump was intended to last for a prolonged period of time extending from a few months up to several years for ambulatory patients who required cardiac assistance for extended periods of time. The procedure required the surgeon to perform a left thoracotomy, cross clamp the aorta, and then fashion a suture line around the perimeter of the patch. An advantage of this configuration was that the geometry of the thoracic aorta is expanded, allowing the displacement volume of the pumping chamber to be in the desired range of 60 cubic centimeters (cc) to 65 cubic centimeters (cc), inclusive, thereby enhancing the clinical effectiveness of the CARDIOVAD® device.
U.S. Pat. No. 5,484,385 discloses an intra-aortic balloon catheter. This patent addresses the potential problem of a thin wall balloon failing by rupture believed to be due to abrasion between the thin wall of the balloon and the inner wall surface of the aorta. Typically, a balloon catheter has a thin wall thickness in order to provide for furling the balloon into a small uniform diameter dimension for surgical insertion through the femoral artery to a position below the aortic arch and the left subclavian artery before unfurling. The patent proposes increased wall thickness and reduced outer diameter of the balloon to provide a narrower tapered distal end of the balloon within the narrower portion of the aorta with the narrower portion of the aorta. However, this patent does not recognize or address the potential tortuosity of the aorta that typically can occur in patients, where the aorta is not smooth and uniform in a two-dimensional plane as depicted in medical books, but rather twists and turns through three-dimensional space within the body cavity creating greater difficulty in properly positioning and operating a balloon pump within the descending aorta of the patient.
U.S. Pat. No. 4,527,549 discloses a method of and means for intra-aortic assist. The patent asserts that the position of the balloon is more important than the size of the balloon, and that the proper position for a balloon is at the root of the aorta right above the valve in the ascending portion of the aorta. In order to traverse the aortic arch, the patent proposes preforming the device to follow the aortic arch. While the patent suggests the use of multi-segment balloons, it specifically teaches that the appropriate position for the first balloon is immediately above the valve in the ascending portion of the aorta. This patent does not recognize the difficulty in positioning a balloon within the ascending portion of the aorta and/or the difficulty in passing a preformed portion corresponding to the arch of the ascending aorta through the serpentine tortuous descending portion of the aorta. The patent does not address the potential clinical danger of stroke created by a catheter moving across the entrances to the arch vessels (e.g. the left subclavian artery, the left common carotid artery, and the innominate artery). The clinical danger of stroke, by way of example and not limitation, can be linked to: (1) risk of dislodgment of embolus or plaque into the arch vessels during insertion of the balloon pump around the arch into the ascending aorta; (2) risk of occlusion of the arch vessels; (3) risk of repeated abrading action against the surface of the arch and entrance to the arch vessels; and (4) risk of dislodgment of embolus or plaque during withdrawal or replacement of the balloon pump. In summary, the patent does not recognize that the risks associated with positioning the proximal balloon in the ascending aorta outweigh the benefits achieved, and that a larger size balloon in the descending aorta alleviates the need to entertain the risk of entering the ascending aorta in order to provide the amount of assistance desired for an ambulatory patient.
U.S. Pat. No. 6,468,200, U.S. Pat. No. 3,791,374, and U.S. Pat. No. 3,504,662 each disclose segmented balloon pumps adapted to be actuated at different rates. For example, U.S. Pat. No. 3,504,662 discloses actuation of the middle compartment prior to or at a more rapid rate than the end compartments. U.S. Pat. No. 6,468,200 discloses the chambers are inflated sequentially beginning with the chamber closest to the aortic root, in order to advance the blood in the downstream direction. Each of these patents teaches the desirability of a temporal sequence of inflation and/or deflation, even though such procedures are of undetermined effectiveness and accordingly are not well established as providing the amount of assistance desired for an ambulatory patient.
An article published by The Society of Thoracic Surgeons in 2002 entitled “Ambulatory Intraaortic Balloon Pump Use as Bridge to Heart Transplant” taught the advantage of using a catheter based intraaortic balloon pump positioned in the descending aorta accessed through an expanded polytetrafluoroethylene vascular conduit graft to the left axillary artery. The procedure allowed the patient to be ambulatory, and allowed multiple exchanges of the catheter based intraaortic balloon pump for extended use (12 days to 70 days). The positioning of the intraaortic balloon was similar to the conventional positioning, except the distal end of the balloon was maintained above the renal arteries and the proximal end of the balloon was positioned just below the subclavian artery in the descending aorta. While pointing out the benefits of maintaining ambulatory patients, the article did not reflect the desirability of increased balloon pump volume for ambulatory patients, and/or the desirability of increased conduit diameter for maintaining balloon pump cycle timing for larger volume balloon pumps, and/or the desirability of a percutaneous access device for connecting the catheter based intraaortic balloon pump to the drive system for an ambulatory patient or the difficulties encountered by chronic abrasion between the straight pumping chambers and the inner wall of the aorta.